The invention described herein relates to a clutch mechanism of the type comprising an input shaft and an output shaft, a primary gear wheel driven by the input shaft, a secondary gear wheel turning with the output shaft, a clutch assembly whose engaging-component may shift axially against the agency of sprung means so as to engage said primary and secondary gear wheels, and a control collar turning with said secondary gear wheel, shifting axially with respect thereto, and assuming both a non-working and a working position, the latter being that in which its action on said clutch engaging-component is brought to bear.
The object of the invention as set forth herein is that of providing a clutch mechanism of the type aforesaid, capable of engaging and disengaging under torque whilst requiring but limited effort for its control.